1. Field of the Invention
The present invention relates to the field of magnetic articles, in particular, to articles which may be applied to a roadway, warehouse floor, and the like, to guide a vehicle or other mobile object thereon.
2. Related Art
Safer, more efficient and more accessible transit for citizens is a high priority for many governments. Public service workers, public transit vehicles and emergency vehicles must have the capability to move more rapidly and safely on roadways in a variety of weather conditions.
Inclement weather and even blinding sunlight or oncoming traffic light present special problems both for existing travel systems and for guidance systems that offer lateral vehicle control. An unfortunate number of tragic accidents have occurred due to people driving under the influence of alcohol and over-the-counter medicines. A magnetic, lateral guidance system addresses the special needs of drivers who cannot, for whatever reason, see the road.
Snowy conditions, fog, heavy rain, blowing dust and smoke are examples of challenges to vehicle drivers. Snowy weather presents particularly challenging driving conditions to snowplow drivers trying to clear lanes in blowing snow or when lane markers are obstructed by snow. Furthermore, reduced visibility brought by blowing snow has caused numerous tragic accidents when automobile drivers have rear-ended snowplows traveling slower than surrounding traffic. Winter weather will continue to challenge any intelligent transportation system (ITS) in which vehicles move at faster speeds and closer together on more crowded roadways.
A magnetic system offers several advantages:
it is not adversely affected by weather conditions;
it does not require expensive video or other radio frequency equipment;
the system""s operating costs remain low since the marker is passivexe2x80x94no power is required to make a magnetic marker function;
the system""s durability means that, once installed, a magnetic marker will likely last beyond the life of the roadway (typical roadways have lifespans of six to eight years) and may even be reprogrammed while still on the roadway; and
removable magnetic markers offer the convenience of being able to remove the marker from the road and xe2x80x9creprogramxe2x80x9d it.
Several alternative methods for sensing the lateral position of a vehicle on a roadway have been suggested. One option involves the use of visible signs or markings and optical sensors. A system that relies on optical sensors can be expected to have reliability problems. The signs or markings can be obscured by dirt, ice, or snow, and visibility can be impaired by fog, blowing snow, blowing dust, and the like. Furthermore, for night usage, a considerable amount of energy must be expended, either to illuminate the signs or to send out a beam from the sensor.
Another approach is the use of radar reflective markers with a radar ranging system on the vehicle. Both the markers and the radar detection systems are expensive in comparison with the magnetic system proposed herein. Metallic radar reflective markers embedded in the roadway are likely to have durability and corrosion problems.
Two known magnetic marking systems deserve attention. One proposal is to use a series of magnetic xe2x80x9cnailsxe2x80x9d embedded in the roadway. Because the field strength decreases as the cube of the distance from such a dipolar magnetic, field source, the xe2x80x9cnailsxe2x80x9d would have to be fairly closely spaced to produce a useful signal. Installation costs would be high since this requires boring holes in the roadway, and materials costs would be very high if the most powerful rare earth magnets were used to minimize the size and maximize the spacing. Boring holes in the roadway may also lead to stress concentration and premature pavement failure, which may be exacerbated by corrosion of nails. The use of simple ferrous metal spikes would not provide the alternating signal desirable for effectively separating the position signal from noise.
Another magnetic marking system employs a magnetic paint to produce magnetic stripes on the roadway. With the typical thickness of paint layers, it would be difficult to obtain a good magnetic signal. If the thickness of the paint were built up to obtain a good magnetic signal, its durability would be poor. The paint stripe could be magnetized only after it had dried. A specially designed magnetizing fixture would have to be driven along the strip. Because of limitations in the magnetic field produced by such a fixture, the coercivity of the magnetic material would have to be limited to about 1000 oersteds, making it susceptible to erasure, and it would be difficult to produce anything other than a longitudinal magnetization pattern.
Conventional conformable non-magnetic pavement marking sheet materials typically comprise a polymeric material, such as one that could be crosslinked to form an elastomer, but which is not crosslinked in the sheet material and thereby provides desired viscoelastic properties. A blend of this material with other polymeric materials and non-magnetic inorganic fillers has been found to provide properties that give long-lasting pavement markings having good conformability to a roadway surface, abrasion resistance, tensile and tear strength. The composition may have glass beads embedded in its upper surface for retroreflective purposes. An example of this type of pavement marking is disclosed in U.S. Pat. No. 4,490,432. Briefly, these advantages can be obtained with a composition that comprises 100 parts of non-crosslinked elastomer precursor; at least 5 parts of a thermoplastic reinforcing polymer (such as a polyolefin) which is dispersed in the elastomer as a separate phase (i.e., because of insolubility or immiscibility with the other polymeric ingredients) and softens at a temperature between about 75xc2x0 C. and 200xc2x0 C.; a particulate inorganic filler dispersed in the composition; and preferably an extender resin, such as a halogenated paraffin. This composition is processable on calendering rolls into a thin sheet material, generally between about xc2xcand 3 millimeters in thickness. The separate-phase nature of the reinforcing polymer is considered desirable, in that it is believed that the polymer becomes oriented during the calendering operation and reinforces the sheet material. Such a reinforcement is indicated by the fact that the tensile strength of the sheet material is significantly stronger in the downweb direction (i.e. in the direction of calendering) than in the crossweb, or transverse, direction.
U.S. Pat. No. 5,316,406 discloses a roadway marker rubber-like strip in which the upper layer is deformed into protuberances such as wedges or ridges, preferably provided with a coating of exposed retro-reflective beads, that have been cross-link-vulcanized to provide the same with memory that permits shape restoration following depression by vehicle traffic, and a cold-flow un-vulcanized bottom layer adhered to the roadway and conforming without memory to the same under vehicle traffic.
Other conformable non-magnetic pavement markings are disclosed in U.S. Pat. No. 4,069,281 (Eigenmann), Italian Patent Application No.MI 003213/91A (which discloses a conformable layer comprising a saturated acrylonitrilel butadiene elastomer grafted with a zinc salt of methacrylic acid), and U.S. Ser. No. 08/056,420 (filed May 3, 1993), which discloses a conformable butadiene layer and at least one resin selected from the group consisting of hydrogenated polycyclodiene resins and aliphatic hydrocarbon resins.
Another approach to pavement markings has recognized that conformability of the pavement marking to the pavement may be enhanced by utilizing a conformable base layer onto which is placed retroreflective elements, either by embedding or by use of a binder layer. In one article, described in U.S. Pat. No. 5,194,113, the conformance layer comprises a ductile thermoplastic polymer (preferably a polyolefin) and a non-reinforcing mineral particulate. Another article, described in U.S. Pat. No. 5,120,154, employs a base layer comprising a microporous thermoplastic polymer characterized by exhibiting certain inelastic deformation/conformability properties.
In none of the above disclosures is the use of magnetic particles disclosed or suggested.
Magnetic installations on roadways and methods of providing control information to vehicles traveling on the roadways are described in, for example, U.S. Pat. No. 3,609,678. This patent refers to useful polymer-based magnetic materials that are elastic to make the material resilient and flexible, such as nitrile and silicone rubbers, and plasticized PVC. The magnetic articles are embedded in the roadway either transverse to the flow of traffic or in the direction of traffic flow. This patent also describes xe2x80x9cwrong-wayxe2x80x9d control systems and systems to control the speed and course of vehicles traveling on the roadway.
None of the known articles or systems discloses or suggests a conformable magnetic article, or suggests a need for such an article.
In addition to vehicles, other mobile objects such as farm animals, pets, fire fighters, visually impaired pedestrians, and the like could also benefit from control and/or guidance systems comprising conformable magnetic articles. Mobile robots equipped with magnetic sensors could be guided and/or controlled as they move on their path, for example, along an industrial assembly line. Perimeter and boundary awareness systems are needed in specific instances. Two examples include warnings of hazardous conditions in the envirornent and pet containment systems. Games frequently require defined boundaries, such as foul territory in baseball and out of bounds in soccer, and it is frequently desired that toys and sporting equipment emit audible signals.
The conformable magnetic articles of the present invention, and systems into which they are incorporated, exhibit a number of advantages over previous approaches, both nonmagnetic and magnetic. Their reliability in all weather conditions should be much better than that of optical systems. The cost of manufacturing and installing the preferred articles (conformable magnetic pavement marking tapes, or xe2x80x9cCMPMTxe2x80x9d) is low relative to other approaches. With modern integrated circuitry, the cost of the detector and associated signal processing is modest, and very little energy would be required for operation. A magnetic material with excellent environmental stability is employed, and durability should be comparable to that of existing pavement marking tapes, which have already been proven in the field. Magnetization could be done at the factory; on site immediately before or after installing the articles; or much later in time after installation of the articles (xe2x80x9crewritablexe2x80x9d or xe2x80x9creprogramablexe2x80x9d), with relatively simple equipment. Materials with coercivities up to 20,000 oersteds can be used, making the inventive articles highly resistant to accidental or deliberate erasure.
Thus, one aspect of the invention is a conformable magnetic (preferably sheet-like) article comprising:
a) an organic binder (preferably comprising materials selected from the group consisting of non-crosslinked elastomeric precursors, thermoplastic polymers (more preferably ductile thermoplastic polymers), and combinations thereof); and
b) a plurality of magnetic particles distributed in the organic binder, the magnetic particles capable of being remanently magnetized and present in an amount sufficient to produce a magnetic field sufficient to be sensed by a: sensor (either one or more, depending on the particular application) and guide and/or control a mobile object moving relative to the article. As defined herein the term mobile object includes human controlled vehicles; humans involved in a variety of activities; farm animals; pets; fire fighters; mobile robots, and the like, all equipped with magnetic sensors having the ability to detect a magnetic signal or signals from the conformable magnetic articles of the invention and convert that signal or signals into an audible, tactile, visual, or other warning and/or control signal.
In one particularly preferred embodiment, the articles of the invention comprise a plurality of magnetic particles distributed within a conformable layer of a conventional pavement marking tape. Preferably, the magnetic particles are oriented physically to increase the remanent magnetization in a preferred direction.
The inventive articles are preferably magnetized in a regular alternating pattern to produce a readily-detectable alternating magnetic signal on the sensor. However, to convey more detailed information, the inventive articles may be magnetized (xe2x80x9cencodedxe2x80x9d or xe2x80x9cwrittenxe2x80x9d) in more complicated patterns, as found in bar codes, credit card strips, or magnetic tape recordings.
The conformable, magnetic articles of the invention (preferably in the form of adhesive-backed tapes) preferably comprise a conformable, magnetic layer containing permanently magnetizable particles such that the magnetic particles of the article can be oriented to produce a magnetic field that is detectable by a sensor mounted on a vehicle, typically mounted at 6 to 12 inches (15-30 centimeters (cm)) above the roadway. The inventive articles preferably produce a magnetic field of at least 10 milligauss at a lateral displacement from the midline of the article of up to 24 inches (61 cm). In tests described in the Examples section herein, it was surprisingly found that one embodiment of the inventive articles produced a magnetic field of at least 10 milligauss at a lateral displacement of about 2 meters (m) from the midline of the inventive article. Typical article width ranges from about 1 cm to 50 cm, preferably 5 to 20 cm, and typical article thickness ranges from about 0.1 cm to about 1.0 cm, preferably about 0.1 to 0.2 cm, although many other article shapes are possible, with shape dictated largely by the specific use of the article.
When controlling /guiding vehicles, articles of the invention may either be placed on the surface of the roadway, or placed in a trench in the roadway. In the latter embodiment, if the surface is a xe2x80x9cfreshxe2x80x9d (i.e. still warm) asphalt surface, or newly deposited, uncured concrete mixture, the articles of the invention may be placed initially on top of the fresh asphalt or uncured concrete and thereafter pushed down substantially flush with the surface using any suitable means such as a roller.
Another aspect of the invention are methods of making the inventive articles. One inventive method comprises the steps of:
a) combining an organic binder precursor with a plurality of magnetic particles, the magnetic particles capable of being remanently magnetized and present in an amount sufficient to produce a magnetic field sufficient to be sensed by a sensor and guide a vehicle moving relative to the article; and
b) exposing the binder precursor to conditions sufficient to form a conformable organic binder having the magnetic particles dispersed therein. Preferably, the product of step b) is further exposed to conditions sufficient to orient the magnetic particles in a desired direction to produce the desired magnetic field (such as exposure to a permanent magnet oar electromagnet). Alternatively, the orientation step may be before the exposure step b).
The term xe2x80x9cbinder precursorxe2x80x9d means an organic material which has not been processed into the final organic binder. Examples of xe2x80x9cexposing the binder precursor to conditions sufficient to form a conformable organic binderxe2x80x9d include cooling in the case of a molten thermoplastic polymer; exposure to an energy source, such as particle radiation (e.g. electron beam) and non-particle radiation (e.g. ultraviolet or visible light), exposure to heat in the case of a thermosetting binder precursor, and the like.
In some organic binder embodiments, for example when the organic binder comprises non-crosslinked elastomeric precursors, traditional rubber processing methods preferably are used to produce the conformable magnetic layer. Typically and preferably compounding is performed in some type of heavy duty, batch or continuous, rubber kneading machine, such as a Banbury mixer or twin screw extruder. The conformable magnetic layer may be formed by calendering between heavy rolls and then slitting to the desired width, directly by extrusion through a die, or by a combination of such methods. If the extruded material is semi-liquid as it leaves the die, the desired magnetic orientation of the magnetic particles may be produced by exposure to a permanent magnet or electromagnet at the exit of the die. If the extruded material is more rubbery than liquid, magnetic orientation using electromagnets may not be successful, but magnetic orientation can often be achieved by mechanical working. Plate-like particles, such as barium hexeferrite, will respond to mechanical working by orienting with their planes in the plane of the sheet. Since the preferred magnetic direction for such particles is perpendicular to the plane, the preferred direction of magnetization of such an article will be perpendicular. Needle-like particles will tend to align with their long axis in the plane. Since the magnetic easy axis (also sometimes termed the xe2x80x9cpreferred axisxe2x80x9d by those skilled in the magnetic arts, both meaning the direction of magnetization of a particle in the absence of an external magnetic field) corresponds to the needle axis, the preferred direction of magnetization for an article containing such particles is transverse or longitudinal. Extensional flow, such as occurs during extrusion, will promote longitudinal orientation at the expense of transverse.
Other article embodiments of the invention, for example those having; separate magnetic and conformable layers; separate uncrosslinked or unvulcanized conformance layers and crosslinked or vulcanized cold-flow layers; keeper layers (which can increase, up to doubling, the magnetic field strength); anti-skid and/or retroreflective layers; and the like, may be made by employing lamination steps, with adhesives being optional between layers, as more fully described with relation to each specific article embodiment herein.
Yet another aspect of the invention is a mobile object control and/or warning system comprising:
a) at least one conformable, magnetic article of the invention, the magnetic particles capable of being remanently magnetized and present in an amount sufficient to produce a magnetic field sufficient to be sensed by a sensor and guide a mobile object moving relative to the article;
b) a sensor which senses the magnetic field produced by the magnetic article; and
c) an indicator (preferably an electronic indicator, for example a visual component, such as a cathode ray tube (CRT) or liquid crystal display (LCD), or audible component such as a horn) which receives an electronic signal from the sensor. In some system embodiments, such as toys, the sensor and indicator are actually the same article, for example when the sensor is a pair of metal strips which are drawn together quickly in the presence of a magnetic field to emit a clicking sound.
Preferably the mobile object is a vehicle, such as a human operated snow-plow, passenger vehicle, truck or the like.
In one preferred vehicle control system embodiment, a magneto-resistive sensor is attached to the underside of a vehicle such that it is approximately 12 inches (30.5 cm) above the road surface. Magneto-resistive sensors useful in the invention can be a variety of sizes; one preferred size is 2xc3x972xc3x973 inches (5.1xc3x975.1xc3x977.6 cm). The output signal(s) from the sensor are transmitted to a display unit preferably via an electric cable, although radio frequency and optical means could also be employed. The display unit is typically located within the view of the driver.
Exemplary system embodiments include a microprocessor, preferably located within the display unit, to perform the required signal processing to convert the sensors"" output signal(s) into a lateral position offset signal. In an open-loop lateral guidance system, this signal is then used to drive an indicator (display, gauge, horn, and the like) for use by the driver in manually adjusting the position of the vehicle. In a closed-loop control system, the signal is used to actuate a controller which exerts an influence on the vehicle, such as adjusting speed, direction, and the like.
Note that the signal processing, while described previously as occurring within the display unit, could alternatively be performed within the sensor unit by moving the microprocessor to that location. If this is done, the output of the sensor unit(s) would be a lateral offset signal, and the function of the display unit would only be to convert this signal to a form suitable for the driver""s needs.
Also note that a microprocessor is not required, that is, the signal processing could be performed using analog electronics, for example, operational amplifiers, trigonometric function generators, and the like.
A method of control and/or guidance of a mobile object using an inventive magnetic conformable article as a component of a system of the invention is another aspect of the invention.
Lateral control of vehicles, especially those operating on crowded highways, requires great precision and accuracy. One key technical step to designing a vehicle lateral control system is defining the procedure to obtain a precision vehicle position fix relative to the road edge or center. Customized firmware and software for the sensor (such as a read only memory) is preferably employed that mathematically convert the signal from the conformable, magnetic articles of the invention (via the sensor) into a lateral offset position of the vehicle on the roadway. The sensor uses control and display electronics to detect and indicate the vehicle""s position to the driver of the vehicle. A device and method useful in the present invention for determining the range and bearing in a plane of an object characterized by a magnetic dipole is described in U.S. Pat. No. 4,600,883 (Egli et al.). This patent describes the mathematics required to derive lateral position based on the strength of the magnetic field components. The mathematics may be reduced to practice via commercially available software, such as a spreadsheet program running on a microprocessor.
One advantage of the inventive magnetic conformable articles lies in the fact that, by appropriate signal processing, the magnetic field produced by the inventive articles and measured by one or more sensors attached to a mobile object can be converted into a signal indicating the position of the mobile object. In systems of the invention that signal is preferably used as a visual and/or audio indicator to the mobile object and/or as an input signal to an automatic control system designed to keep the mobile object in a fixed position, such as in a lane on a highway. An example of a visual indicator would be a gauge on the dashboard of a snowplow vehicle, showing the snowplow operator how far to the right or left the operator was of the center of the lane to be plowed (or how close to the edge of the lane). An example of an audio signal would be a loud alarm that would go off next to the driver of a truck when the truck started to veer off of the roadway onto the shoulder, possibly as a result of the truck driver falling asleep. The automatic control system might function as a component of an intelligent vehicle system (IVS), in which vehicles are automatically controlled to move in fixed lanes at fixed speeds and spacings, such as in an intelligent vehicle highway system (IVHS) or intelligent transportation system (ITS). This magnetic system offers cost advantages over optical-based approaches, and in addition can be functional when optical systems are incapacitated, such as during inclement weather.
By magnetizing the strip in a more complicated pattern, additional information can be encoded. For example, information about the direction and radius of an upcoming curve in the road or about the slope of an approaching upgrade or downgrade could be used for feed-forward control of the lateral position and speed of the vehicle. As part of a vehicle navigation system, location codes could be given.
Further aspects and advantages of the invention will become apparent from the drawing figures, description of preferred embodiments, examples, and claims.